1. Field of the Invention
The present invention relates to a motor-drive unit having a heat radiator for releasing heat from a semiconductor device mounted on a substrate.
2. Description of the Related Art
Generally, in a case that a circuit of a motor-drive unit having a heat radiator is designed by using one printed board, an area of the motor-drive unit viewed in a front direction (or a direction perpendicular to the printed board) is approximately equal to the printed board when the printed board is attached to the motor-drive unit. Therefore, depending on the area of the printed board, the motor-drive unit (or the heat radiator) is enlarged. For example, Japanese Unexamined Patent Publication (Kokai) No. 2002-246779 discloses a heat sink to which two circuit boards orthogonal to each other are attached, in order to reduce a volume occupied by the entire heat sink.
Further, as another example for downsizing a heat radiator, Japanese Unexamined Patent Publication (Kokai) No. 2010-187504 discloses an inverter unit wherein a capacitor board on which a capacitor is mounted and a printed board on which a semiconductor device is mounted are attached to different planes of a heat radiator, in order to thermally separate the capacitor board from the printed board.
In the heat sink as described in Japanese Unexamined Patent Publication (Kokai) No. 2002-246779, the circuit board is fixed to the heat sink at a single site thereof, or the circuit board is configured as a cantilever structure. Therefore, the fixing of the circuit board may be unstable. Further, since each circuit board is independent from each other, the area of the board in the front direction may be increased depending on a design of the circuit, whereby the width of the board in the front direction may be increased.
On the other hand, in Japanese Unexamined Patent Publication (Kokai) No. 2010-187504, the capacitor board is positioned at a lateral side of the heat sink. However, since the smoothing capacitor has a certain height in order to have a predetermined capacitance, even when the capacitor board is positioned at the lateral side of the heat sink, the width of the board in the front direction cannot be significantly decreased.